import { FlattenConcurrentSelector, FlattenConcurrentAsyncIterable } from './_flatten.js';
import { OperatorAsyncFunction } from '../../interfaces.js';

/**
 * Projects each element of an async-iterable sequence to an async-iterable sequence,
 * emitting values only from the most recently projected async-iterable sequence.
 *
 * @template TSource The type of the elements in the source sequence.
 * @template TResult The type of the elements in the projected inner sequences and the elements in the merged result sequence.
 * @param {((
 *     value: TSource,
 *     index: number,
 *     signal?: AbortSignal
 *   ) => AsyncIterableInput<TResult>)} selector A transform function to apply to each element.
 * @param {*} [thisArg] Option this for binding to the selector.
 * @returns {OperatorAsyncFunction<TSource, TResult>} An operator that creates an async-iterable sequence whose
 * elements are the result of invoking the one-to-many transform function on each element of the input sequence.
 */
export function switchMap<TSource, TResult>(
  selector: FlattenConcurrentSelector<TSource, TResult>,
  thisArg?: any
): OperatorAsyncFunction<TSource, TResult> {
  return function switchMapOperatorFunction(source) {
    return new FlattenConcurrentAsyncIterable(source, selector, 1, true, thisArg);
  };
}